Key tuning apparatus for electronic musical instruments



Sept. 20, 1 R. H. PETERSON KEY TUNING APPARATUS FOR ELECTRONIC MUSICAL INSTRUMENTS 4 Sheets-Sheet 1 Filed March 23, 1959 6 AMPLi Fl EP It? Jar-afar fi l rd AK Pei erg at? Sept. 20, 1960 R. H. PETERSON 2,953,053

KEY TUNING APPARATUS FOR ELECTRONIC MUSICAL INSTRUMENTS Filed March 25, 1959 4 Sheets-Sheet 3 g AMPLIFIER 5 ";E;' l I I EJ491152?! f zmzox'd Al ei'ers an Giztoyrzev p 20, 1950 R. H. PETERSON 2,953,053

KEY TUNING APPARATUS FOR ELECTRONIC MUSICAL INSTRUMENTS Filed March 25, 1959 4 Sheets-Sheet 4 AMPLIFI EE I l l l l l E XO ITEE y/4 l l l l 47 a4; J04 91 I 7 V 100 United States Patent Ofiice KEY TUNING APPARATUS FOR ELECTRONIC MUSICAL INSTRUMENTS Richard H. Peterson, 10108 Harnew Road E., Oaklawn, Ill.

Filed Mar. 23, 1959, Ser. No. 801,223

12 Claims. (Cl. 84-117) This invention relates to electrical musical instruments, particularly to instruments of the organ type, that employ a plurality of electrical oscillators to produce tone signals of frequencies corresponding to the notes of the musical scale. More specifically, it relates to organs employing oscillators of the type that are normally not in oscillation, but that are rendered operative by the application of actuating potential through switches selectively controlled by the playing keys of the instrument. Such organs ordinarily employ large numbers of oscillators, generally one for each note of the musical scale over a range of several octaves. A complete organ, therefore, generally requires at least sixty and preferably seventy-two or more oscillators for even the smallest single key-board instrument.

One object of the invention is to provide a complete musical instrument that requires a greatly reduced number of oscillators but that nevertheless is capable of substantially the same musical performance as organs employing a separate oscillator for each note. Systems for making organs requiring less than one oscillator per note are well known and are substantially as old as the art itself, but no system has been completely satisfactory for use in high-quality instruments, and as a result of the limitations of these known systems, they have been employed only to a limited extent, and only in very simple low-cost instruments capable of rather limited musical performance.

In common with the relatively ineffective devices of the prior art, this invention takes advantage of the Wellknown fact that in ordinary organ literature, of either the popular or the classical variety, adjacent semi-tone frequencies are almost never known to be sounded at the same time. Therefore all such music could be produced with two of the key-board keys for adjacent semi-tones sharing the same oscillator because they will never be played at the same instant.

One objection to traditional shared-oscillator systems is that the switching apparatus required to utilize such oscillators in organs is generally quite complex, and therefore, if it is desired to employ such traditional organ effects as octave couplings and the like, the total switching apparatus becomes excessively complicated to the extent that the additional switching equipment may well be a greater drawback than the cost of providing the extra oscillators. It is another object of this invention, therefore, to provide an oscillator capable of supplying any one of a plurality of notes of the musical scale, wherein the switching apparatus required is no more complicated than it would be in organs employing separate oscillators for each note.

Another objection to known shared-oscillator systems is that the decay characteristics of the tones were influenced adversely by the sharing of the oscillator. Therefore, it is a further object of this invention to provide a shared oscillator system wherein desirable musical decay characteristics can be secured without interfering 2,953,053 Patented Sept. 20, 1960 with tuning the oscillators to their various selected pitches.

Further objects and advantages of the invention will become apparent as the description proceeds.

In the accompanying drawings:

Figure 1 is a schematic wiring diagram of one oscillator of a shared oscillator system of the conventional yp Figure 2 is a similar wiring diagram for one type of shared oscillator according to the invention;

Figure 3 shows a further development of the new inventive principle involved;

Figure 4 shows a more complete development, with respect to reducing the number of key switches;

Figures 5 and 6 show two more variations of voltage dependent resistors.

The oscillator of Figure 1 comprises essentially a tuned LC loop having an inductor 10 connected across the terminals of a capacitor 12.

Oscillations are set up in this loop 11, as by exciting means 14 coupled to the loop terminals 16 and 18. The exciting means may be of any well-known type, such as a vacuum tube or a transistor.

United States Patent 2,649,006 shows one suitable vacuum tube exciter. With these or any other equivalent exciter, an energy source 20 is needed to deliver appropriate activating potential to the activating terminal 22 of the exciter. With the well-known vacuum tube a common activating potential is from plus to plus 300 volts D.C. With a transistor exciter the voltage is 27 volts or less and may be either plus or minus. In Figure 1 the terminal 22 may receive activating potential from the source 20 through circuits set up by either of two adjacent playing keys, a playing key 24 for sounding one pitch, such as middle C, also called C and a playing key 26 for sounding a pitch one semi-tone higher, C3 Ground is identified by the reference character 28 and all of the ground connections illustrated in the drawing are to the same ground. Associated with key 26, to be mechanically closed by depressing the key and opened by releasing the key, is a key switch 30 connected to the ungrounded terminal of source 20 and to the activating terminal 22. Depression of key 26 will therefore deliver activating potential to the terminal 22 and the exciting means will initiate and maintain oscillation in the loop 11 as long as the key remains depressed. When the operators finger is removed from the key the key will rise and the switch will open and the tone will stop. The frequency of this tone is substantially a mathematical function of the magnitudes of the inductor 10 and the capacitor 12. It is customary to tune the entire oscillator by adjusting either the inductance or the capacitance in the loop and I have indicated a ferromagnetic core at 32 which is adjustable, as diagrammatically indicated by the arrow 34. U.S. Patent 2,818,759 discloses the details of such tuning means.

With the tuning loop adjusted to deliver the note Gig in the conventional way through protective resistance 36 to translating means including the amplifier 38 and the loudspeaker 40, the means for causing the same oscillator to sound the note C one semi-tone lower, comprises a much smaller capacitor 42 which may be connected in parallel with the capacitor 12 to add its storage capacity to that of the capacitor 12 and lower the inherent frequency of the oscillator itself to the precise degree necessary to secure the different and lower pitch. To accomplish this two switches are associated with the key 24. The switch at 44 receives the same potential as the switch 30 and delivers it through conductor 46 to the appropriate terminal of the switch 30 and from there the current continues to terminal 22 as before.

A switch 48 of similar construction is electrically separate from the switch 44 but is mechanically depressed and closed by the same key 24. This switch connects one terminal of the capacitor 42 through the switch 48 to ground at 28, and the other terminal is connected by a conductor 50 to point 52 of the tuned loop .11. Closure of the switch 48 and the switch 44, therefore, energizes the exciting means and simultaneously includes the capacitor 42 so that the oscillator delivers the note C Furthermore, if the key 26 is depressed at a time when the key 24 is being held closed, neither the hearer nor the oscillator will know the difference. In either case terminal 22 continues to receive activating potential and the repeated closing and opening of the key 26 will be entirely without elfect. I

However, the reverse is not true at all. With key 26 depressed andnote C4 sounding, depressing key 24 will move the frequency down to C and release of the key 24 will move the frequency up again.

If this were all that is required in the rendering of conventional organ music of moderate complexity, there would be no need for the present invention. But with conventional instruments and with conventional music, when a note is being discontinued it does not cut itself off abruptly, with such a click as is commonly experienced when a telephone receiver is lifted or hung up, but the sound dies away gradually over a period that may vary from a fraction of a second up to three or four seconds. It is desirable for the electronic instrument to provide a slow decay when desired by the player, to get the right esthetic elfect.

In Figure l I have indicated a capacitor 52" connected between the exciting terminal 22 and ground. It will be obvious that when either key 24 or key 26 is depressed the energy of the source 20 will not only maintain the functioning of the exciting means and oscillator but it will charge capacitor 52" up to its own full potential. Subsequently, when the playing key is released, this stored energy remains available at the terminal 22 to replace the source 20 momentarily and the sound will continue until this energy has been used up. But the decreasing potential resulting from the gradual discharge of the capacitor 52" will cause the sound to decrease in intensity much as an ordinary musical note dies away. Various expedients are used to enable the player to change the amount of energy stored in such a capacitor to secure varying percussion effects, but no music is acceptable in which the minimum continuation of sound is not appreciable.

Consider now the equipment according to Figure l in which the capacitor 52" is of a size to produce a decay period of one second, and let the player play staccato notes having a duration of one-quarter of a second. If the key 26 is momentarily depressed and released again, there will be the predetermined decay period and the oscillator will continue to speak with a decreasing volume of sound down to Zero at the end of a second. If the key 24 is depressed after the key 26 has been released but before the end of the decay period for the note Ci the inception of the new sound will mask and obscure the disappearance of the previous frequency to such an extent that the result is not offensive to the ear. However, every time the key 24 is depressed for either a quarter of a second or for any length of time whatsoever, when the key 24 is released, the release removes the capacitor 42 from the circuit with the abruptness of a telephone receiver being slammed down and the oscillator will decay in C4 which changes the pitch one semi-tone in an unnatural way at the instant key 24 is released. No teenage boy whose voice is changing and unexpectedly shifts into falsetto can rival the absurdly grotesque eifect that is produced in this way. No such freak noises can be tolerated in the production of music. Therefore the size of capacitor 5 has to be almost nothing. But to simulate correctly the performance of an ordinary organ pipe requires a decay time that may be quite short, but not nearly as short as must be used with circuitry according to Figure 1.

In Figures 2, 3, and 4, I have indicated three embodiments selected to illustrate the invention. All of these achieve complete musical adequacy, so far as the player is concerned. The embodiment of Figure 4 also achieves musical adequacy with no additional key switches.

It will be noted that the entirety of the oscillator proper may be identical with that of Figure l, but the switching means associated with keys 24 and 26 is substantially reorganized.

Key switch 24 closes switch 44 and another switch 54 corresponding to switch 48, in Figure 1. From the switch 54 potential passes through resistor 41 to terminal 43 and then through resistor 45 to terminal 47.

Resistors 41 and 45 are merely protective, to avoid sparking at the switch contacts by fully instantaneous discharge of capacitor 70. They also protect against short circuiting the source 20 when keys 24 and 26 are both depressed at the same time.

Terminal 47 is connected to electronic means for rendering the path from tuning capacitor 42 to ground 28, conductive or non-conductive to the A.C. signal in loop 11. Figures 2, 3, 4, 5 and 6'indicate five different types of electrical network for doing this.

In Figure 2 the non-polar voltage sensitive resistor 66 is of the type more fully disclosed for use as a distor-ter in US. Patent 2,649,006. At zero voltage, the resistance is at a predetermined high value. Application of voltage lowers the resistance smoothly without any discontinuity, to values of from one one hundredth to one one thousandth of the high resistance obtaining at zero voltage.

Capacitor 42 is connected to a junction 68. From terminal 47, the DC). circuit runs through voltage sensitive resistor 66 to terminal 68, and from there to ground through two paths. The low resistance path is through rectifier and biasing battery 71. The high resistance path is through resistor 73, shunted around capacitor 42, conductor 50, and inductance 10, to ground.

Resistor 73 is of relatively high resistance. It is employed as a safeguard to make sure that biasing battery '71 keeps the potential drop at diode 69 in the direction of high resistance and at all times not less than maximum signal voltage. Theoretically, such a rectifier diode should bias itself by rectifying the signal from the capacitor 42, but some commercial diodes are not sufficiently dependable to be relied on for such a critical function, in which case I employ the double safeguard of adding the battery 71 and high reactance shunt 73.

When potential is supplied from source 20, the potential at point 68 changes enough to start a current flow through battery 71, in a direction opposite to the of that battery. Rectifier 69 becomes conductive and resistor 66 drops to its low resistance condition. The A.C. signal from capacitor 42 now passes freelythrough diode 69 and battery 71 to ground. There is also a parallel A.C. ground through resistors 66, 45 and capacitor 70. Capacitor 42 is now effective to lower the frequency of the loop 11, and the oscillator will deliver the note C 7 g The capacitors 12 and 42 are a commercial product and it is difficult to produce them at reasonable cost, with an accuracy better than 5%. The overall adjustment of the entire loop is taken care of by adjusting the inductor at 34. Then a capacitor 42 is selected from stock, of a size that will lower the overall pitch about of a semi-tone. Trimming capacitor 39 in series with an adjustment resistor 37 is shunted around capacitor 42, and a final high precision adjustment is made at the factory on the resistor 37. It would be possible to get equivalent adjustment of pitch with a series resistor in conductor 50, but that would dissipate energy in 5 the main signal and impair the functioning of the entire oscillator.

T provide the note C with a decay period of proper length, a capacitor 70 is connected from junction 43 to ground 28. When potential is first supplied, this capacitor picks up a full charge, and when key 24 is released, the charge on capacitor 70 cannot be dissipated through the switch 44 and will, therefore, cause a current through resistor 66 and diode 69 to ground. Thus, the capacitor 70 keeps the resistor 66 at its low value and the diode 69 conductive and the capacitor 42 operative at least as long as capacitor 52 sustains the oscillation of the exciter itself, and a normal decay of unchanged C frequency results.

When the player depresses key 26, potential arrives at terminal 22 through the key switch 30 as in Figure 1.

When key 26 is depressed and the key 24 is also depressed before the normal decay period for the note Cil has ended, the note C takes over and the acoustical effect is not objectionable, just as in Figure 1.

But when key 24 is depressed and subsequently key 26 is depressed before resistor 66 has resumed its high resistance condition, the player might be unable to sound the note Cil as soon as required by the music. To eliminate this interference, I provide a cutout switch 74 mechanically closed by key 26. This switch grounds one end of a conductor 76, and the other end of the conductor is connected at junction 47. Now when key 26 is depressed before the tone resulting from depressing key 24 is at an end, the potential at junction 47 drops instantaneously to zero and the resistor 66 resumes its high resistance value and the oscillator 11 assumes the frequency Cri It will be apparent that with wiring according to Figure 2, rapid chromatic runs, or semi-tone trills, can be executed by the player at will, and the instrument will keep up with the players fingers at all times.

Referring now to Figure 3, key 24 closes switch 44 as in Figures 1 and 2 but the activating potential is delivered by switch 44 to a tuning terminal 56. From the terminal 56 potential passes through the diode 58 to terminal 22 and the oscillator receives the same exciting impulse as before. From the tuning terminal 56 potential passes also through the diode 60 to resistors 41, 45 and 66, as in Figure 2.

When the potential of the source 20 is delivered to the tuning terminal 56, in Figure 3, it initiates a DC. current flow through the ordinary resistors 41 and 45, and voltage sensitive resistors 66 and 73. A.C. signal passes freely to ground through both 73 and 66 and capacitor 42 becomes effective to lower the frequency of the loop 11, and the oscillator will deliver the note C This circuit would be fully operative if resistor 66 were an ordinary resistor, but with both resistors 73 and 66 sensitive to voltage, a lower and more convenient working voltage becomes adequate. The same is true in Figure 2, and in Figures 4, 5 and 6, resistor 45 could be made voltage sensitive.

As in Figure 2, the capacitor 70 is connected from junction 43 to ground 28. When potential is first applied, this capacitor picks up a full charge, and when key 24 is released, the capacitor 70 keeps the resistors 66 and 73 at their low values and the capacitor 42 operative at least as long as capacitor 52 sustains the oscillation of the exciter, and a normal decay of unchanged C frequency results.

When the player depresses key 26, potential arrives at terminal 22 through the key switch 30 as in Figure 1, but this potential is blocked by rectifier 58 and all the circuitry from there to capacitor 42, and resistor 73- gets nothing and performs no function. This gives the note C4 and releasing the key 26 will give a normal Cii decay.

When key 24 is depressed and subsequently key 26 is 6 depressed before resistor 66 has resumed its high re sistance condition, the player might be unable to sound the note Cil as soon as required by the music. To eliminate this interference, I provide the cutout switch 74 as in Figure 2.

Referring now to Figure 4, the oscillator proper is still unaltered, and the tuning contact 56 and diodes 58 and 60 remain the same. The key 24 and its associated circuits also remain unchanged. The switch 74 and conductor 76 of Figure 3 have been replaced by a diode 77 between switch 30 and terminal 22. I have also replaced resistors 66 and 73 with a biased diode 78.

When key 24 is depressed, potential is delivered through switch 44 tuning terminal 56 and diode 60 to the resistors 41 and 45, and to capacitor 70.

From junction point 68 the cut-in circuit runs through diode 78 and resistor 84 to ground 28. The rectifier 78 is bridged by a biasing circuit including potential source 86 and resistor 88. When key switch 44 is open, potential source 86 imposes a voltage on diode 78 opposite to the direction in which current can flow and greater than any signal voltage that might come to junction 68 through capacitor 42.

When key 24 is depressed, the greater potential of source 20 will come to terminal 68 and overcome the potential of source 86, and rectifier 78 will become conductive and render capacitor 42 effective to lower the frequency of loop 11. The subsequent release of key 24 will leave the capacitor 70 charged to keep the rectifier 78 conductive at least as long as capacitor 52 keeps the exciter 14 in oscillation. But if switch 30 is closed before key 24 is released, or before the tone resulting from key 24 has decayed, the potential at junction 89 delivered by conductor 91 will immediately reverse the potential on rectifier 78, and interrupt the functioning of capacitor 42. Again rapid trills, or runs, in either direction, can be executed, and the oscillator will keep up with the fingers of the player just as in Figure 2. However, all these functions are obtained with only one switch contact for each key so that the multiple contact difficulty is also eliminated.

In Figure 5 I have indicated the junction point 68 connected through a neon tube 90 in series with a protective resistor 94.

When the voltage of source 20 comes to point 68, the tube 90 breaks down and DC. and A.C. current passes freely through the tube 90 and resistor 94. The cut-out circuit wire 91 may be connected at junction 98. It will be obvious that resistors 84 in Figure 4 and 94 in Figure 5 must both be quite low to enable capacitor 42 to function with full effect.

In Figure 6 I have indicated a cadmium sulphide photoresistor at 100, and a miniature incandescent light source 102, connected to receive potential from terminal 47, and protected by resistor 104. The cut-out circuit wire 91 may be connected to junction 106. The cadmium sulphide photo-resistor can be made to change its resistance over ratios as high as 1,000,000 to l or even 1,000,000,000 to 1, or more by merely changing the amount of light impinging on the same.

The complete tone generator of an organ according to the invention will include the collecting bus 108 and as many additional protective resistors 110 as there are oscillators.

Summarizing the operation of Figure 4, the first key 26 has a first activating circuit running from the potential source 20 through the switch 30 and rectifier 77, to the terminal 22. The second key 24 has an activating circuit from the same source 20 through the switch 44 and terminal 56 and branching there from the rest of the activating circuit to pass through the rectifier 60, the resistors 41 and 45, biased rectifier 78, and resistor 84, to ground at 28. The tuning circuit for lowering the frequency of the exciter is from terminal 52, through capacitor 42 to terminal 68 and from there on in common with the cut-in circuit to ground. Only one more keying circuit is needed, to cut out the tuning circuit and render it inoperative whenever the first key 26 is depressed. This is a branch circuit from the source, through switch 30 and cross connection 91 to the terminal at 89.

Whenever terminal 22 receives activating voltage the oscillator functions and capacitor 52" stores the appropriate amount of energy for providing the desired decay rate of the oscillation after activating potential is withdrawn. And whenever the cut-in circuit is activated by depressing key 24 capacitor 70 also stores energy, which energy becomes available after activating potential is withdrawn to continue the operativeness of the cut-in circuit at least as long as capacitor 52" continues the oscillation of the oscillator.

It will be seen that in Figure 1 each key has an activating circuit individual to that key, but the two circuits may have certain parts in common. There is also a third, tuning circuit, which contains capacitor 42 and is controlled by key switch 48.

In each of Figures 2 to 6, there are two additional circuits, consisting of a cut-in circuit for rendering the tuning circuit operative, and a cut-out circuit for rendering the tuning circuit inoperative.

In Figures 2, 3, 4 and 5, part of the cut-in circuit is part of the tuning circuit also, but in Figure 6 the operative connection is optical rather than electrical, and the tuning circuit and cut-in circuit are electrically separate and distinct.

This application is a continuation-impart of my copending application S.N. 596,544, filed July 9, 1956, now Patent 2,906,959, issued September 29, 1959.

Others may readily adapt the invention for use under various conditions of service by employing one or more of the novel features disclosed or equivalents thereof.

It will be obvious that the different types of cut-in circuits disclosed may include some which are best adapted to deal with notes of low pitch, and others which get the best results for notes of high pitch, and that ditferent segments of a single keyboard may each have its own preferred type of cut-in circuit.

As at present advised, with respect to the apparent scope of my invention, I desire to claim the following subject matter:

1. In an electronic organ, in combination, an oscillator comprising a tuned LC loop circuit and an exciter operatively associated with said loop and adapted, upon receipt of activating potential, to initiate and maintain oscillation in said loop as long as activating potential is supplied; said exciter having a terminal for receiving activating potential; a tuning circuit adapted to change the frequency of said oscillator from one pre-selected note of the musical scale to a difierent note; first and second playing keys corresponding to unchanged and changed frequencies of said oscillator, respectively; first and second switch contacts, one for each key, respectively; a first activating circuit rendered operative by said first switch contact for delivering activating potential to said oscillator terminal; a second activating circuit rendered operative by said second switch contact for delivering activating potential to said oscillator terminal; a cut-in circuit rendered operative by depressing said second key, for rendering said tuning circuit operative; said tuning circuit being otherwise inactive, and inoperative to change the oscillator frequency; a cutout circuit rendered operative by depressing said first key for rendering said cut-in circuit inoperative; a source of activating potential for each of said switch contacts; a first energy storage means connected to said oscillator and adapted to have its energy content changed when activating potential is delivered to said terminal and to resume its initial condition by means of current through said oscillator after activating potential is withdrawn; whereby said oscillator continues to oscillate with decreasing amplitude for a predetermined time; a second energy storage means connected to said cut-in circuit and adapted to have its energy content changed when activating potential is present in said cut-in circuit and to resume its initial condition by means of current through said cut-in circuit after activating potential is withdrawn; whereby said cut-in circuit remains operative for a pre-determined time after activating potential is withdrawn; said second energy storage means being adapted to keep'said cut-in and tuning circuits operative after activating potential is withdrawn, at least as long as said first energy storage means maintains oscillation in said oscillator; said oscillator having an output circuit for delivering signal; and translating means for translating said output signal into musical sound.

2. A combination according to claim 1 in which said changed frequency is lower than said unchanged frequency by one musical semi-tone.

3. A combination according to claim 1 in which a single potential source is connected to supply activating potential to both activating circuits.

4. A combination according to claim 1 in which a single potential source is connected to supply the same activating potential to both activating circuits, and to said cut-in and cut-out circuits.

5. A combination according to claim 1 in which both said activating circuits contain substantial rectifiers adjacent to said activating terminal, for preventing the re ception of activating potential from said terminal.

6. A combination according to claim 1 in which said cut-in circuit comprises a non-polar voltage sensitive resistor connected in series in said tuning circuit; and connections for applying DC. potential to said resistor to reduce its resistance and render it conductive to AC. signal.

7. A combination according to claim 1 in which said cut-in circuit comprises a. substantial rectifier connected in series in said tuning circuit; biasing means for applying to said rectifier a potential difference in the direction of high resistance; said biasing means potential being greater than maximum signal potential; and means for delivering to said rectifier a second potential in the direction of low resistance; said second potential being greater than the sum of biasing means potential and maximum signal potential, to keep said rectifier continuously conductive to signal.

8. A combination according to claim 1 in which said cut-in circuit comprises a gas-filled tube and a potential source; said tube and source being connected in series in said timing circuit, with said source applying a voltage in the direction of conduction of said tube, but less than enough to maintain discharge in said tube; and means for applying to said tube additional voltage in the same direction, up to a total voltage greater than the breakdown voltage of said tube.

9. -A combination according to claim 1 in which said cut-in and cut-out circuits are each controlled by their respective keys by means of additional key switches in sulated from each other and from said first and second switch contacts.

10. A combination according to claim 1 in which said cut-in circuit comprises a cadmium sulphide photo-resistor connected in series in said timing circuit, and a light source responsive to source potential for illuminating said resistor.

11. A combination according to claim 10 in which said light source is a miniature incandescent filament.

12. In an electronic organ, in combination, an oscillator comprising a tuned LC loop and an exciter operatively associated with said loop and adapted, upon receipt of activating potential, to initiate and maintain oscillation in said loop as long as activating potential is supplied; said exciter having a terminal for receiving activating potential; a tuning circuit adapted to change the frequency of said oscillator from one pro-selected note of the musical scaleto a different note; first and second playing keys corresponding to the unchanged and changed frequencies of said oscillator, respectively; first and second switch contacts, one for each key respectively; a first activating circuit rendered operative by said first switch contact for delivering activating potential to said oscillator terminal but not for receiving activating potential from said oscillator terminal; a second activating circuit rendered operative by said second switch contact for delivering activating potential to said oscillator terminal but not for receiving activating potential from said oscillator terminal; a cut-in circuit rendered operative by activating potential in said second activating circuit for rendering said tuning circuit operative; said tuning circuit being otherwise inactive, and inoperative to change the oscillator frequency; a cut-out circuit rendered operative by activating potential in said first activating circuit for rendering said cut-in circuit inoperative; a source of activating potential for each of said switch contacts; a first energy storage means connected to said oscillator and adapted to have its energy content changed when activating potential is delivered to said terminal and to resume its initial condition by means of current through said oscillator after activating potential is withdrawn; whereby said oscillator continues to oscillate with decreasing am plitude for a predetermined time; a second energy storage means connected to said cut-in circuit and adapted to have its energy content changed when activating potential is present in said cut-in circuit and to resume its initial condition by means of current through said cut-in circuit when activating potential is withdrawn; whereby said cut-in circuit remains operative for a pre-determined time after activating potential is withdrawn; said second energy storage means being adapted to keep said cut-in and tuning circuits operative after activating potential is withdrawn, at least as long as said first energy storage means maintains oscillation in said oscillator; said oscillator having an out-put circuit for delivering signal; and translating means for translating said output signal into musical sound.

References Cited in the file of this patent UNITED STATES PATENTS 2,357,191 Hancrt Aug. 29, 1944 2,579,358 Bourn Dec. 18, 1951 2,790,906 Hammond Apr. 30, 1957 2,905,905 George Sept. 22, 1959 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2 953 O53 September 20, 1960 Richard [-1. Peterson It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 8 lines 49 and 62 for "timing", each occurrence read tuning Signed and sealed this 11th day of April 1961.

(SEAL) Attest ERNEST W. SWI DER ARTHUR W. CROCKER Attc'sging Oflicer Acting Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2 953 O53 September 20, 196

Richard H. Peterson It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 8, lines 49 and 62 for "timing", each occurrence read tuning Signed and sealed this 11th day of April 1961 (SEAL) Attest -3 WAS-WIDER ARTHUR W. CROCKER Atteeting Oflicer Acting Commissioner of Patents 

